Processes for reforming hydrocarbons to produce a reformed gas composition comprising synthesis gas, also called syngas, are known in the art and include steam reforming, catalytic dry reforming, partial oxidation or combinations thereof.
Steam reforming of hydrocarbons is a well known method for producing syngas and involves contacting the hydrocarbon with steam. Steam reforming is highly endothermic and requires high reaction temperatures of e.g. 700-1100° C. Accordingly, care should be taken to avoid thermodynamic constraints. Furthermore, steam reforming of hydrocarbons requires relatively long contact times. Typically, the syngas mixture produced by steam reforming of a hydrocarbon such as methane has a very high H2/CO ratio of approximately 4.5-5.2. The H2/CO ratio of syngas produced by steam reforming methane may be adapted e.g. by adding CO or by removing H2. Alternatively, the H2/CO ratio of a syngas composition may be adapted to a desired value by subjecting it to the reverse water-gas shift reaction.
A syngas composition with a H2/CO ratio of approximately 1 can be produced directly by catalytic dry reforming of methane with CO2. Also catalytic dry reforming of methane is highly endothermic and should be executed at high reaction temperatures. Many catalytic dry reforming processes are known to involve rapid coke deposition leading to catalyst inactivation. In these catalytic dry reforming processes the reactor can be regenerated by feeding oxygen to the catalyst under high temperatures.
Partial oxidation in the presence of a hydrocarbon feed is a further means to produce a syngas mixture. A disadvantage of partial oxidation is that carbon dioxide is produced as a by product, which limits the selectivity for aliphatic and aromatic C2-C6 hydrocarbons of the hydrocarbon reforming process.
By combining different reforming reactions including those described herein above, the reforming process can be optimized e.g. by circumventing thermodynamic constraints and/or by reducing the costs for heating or process heat removal.
A particularly advantageous combined reforming process for producing syngas is catalytic autothermal dry reforming of lower hydrocarbons such as methane. By contacting a mixture of methane (CH4), oxygen (O2) and carbon dioxide (CO2) with a catalyst, endothermic dry reforming and exothermic methane oxidation can be performed in a single regime, which represents an effective means to decrease the energy consumption during syngas synthesis; see e.g. MORTOLA, et al. Eds. NORONHA, et al. Elsevier, 2007. p. 409-414. A further advantage of autothermal dry reforming is that the H2/CO ratio of the produced syngas composition is approximately 1.4-1.8, which is highly advantageous for the further use of the produced syngas in processes such as Fischer-Tropsch (F-T) synthesis.
It has been described that also nickel-based catalysts may be used in a process for the partial oxidation of light hydrocarbons to syngas. Particularly, catalysts comprising nickel supported on lanthana are known to allow a relative high conversion and selectivity in a process for producing syngas from light hydrocarbons; see e.g. EP 741107 A; U.S. Pat. No. 5,447,705 and US 2004/0127351.
A drawback when using a conventional Ni/La2O3 reforming catalyst in autothermal dry reforming of e.g. methane is deactivation of the catalyst, at least partially due to coke formation. This catalyst deactivation leads to a reduced hydrocarbon selectivity and reduced process economy.
The technical problem underlying the present invention is the provision of an improved catalyst useful in a process for converting hydrocarbons such as methane to syngas.